The objectives of this proposal involve extension or initiation of the x-ray crystallographic structure determinations of the following proteins: 1) Chl. thiosulfatophilum cytochrome c555, a primitive c-type cytochrome 2) Bacterial cytochromes c', which are high-spin dimeric heme proteins 3) Chromatium flavocytochrome c552, a complex alpha beta dimer catalyzing the cytochrome c dependent oxidation of sulfide 4) C. Adamanteus phospholipase A2, a dimeric membrane hydrolyzing enzyme, and 5) E, coli recA protein, involved in DNA recombination and repressor proteolysis.